In a UMTS (Universal Mobile Telecommunications System) network, for the purposes of improving spectral efficiency and improving the data rates, system features which are based on W-CDMA (Wideband Code Division Multiple Access) are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). For this UMTS network, for the purposes of further increasing spectral efficiency and the peak data rate, reducing delay and so on, long-term evolution (LTE) has been under study (non-patent literature 1).
Unlike W-CDMA, LTE uses, as multiplexing schemes, OFDMA (Orthogonal Frequency Division Multiple Access) on the downlink, and SC-FDMA (Single Carrier Frequency Division Multiple Access) on the uplink.
As shown in FIG. 1, a signal to be transmitted on the uplink is mapped to adequate radio resources and transmitted from user terminals (UE (User Equipment) #1 and #2), to a radio base station apparatus. In this case, user data is allocated to an uplink shared channel (PUSCH: Physical Uplink Shared Channel). Also, when control information is transmitted at the same time with user data, the control information is multiplexed with the PUSCH, and, when control information alone is transmitted, the control information is allocated to an uplink control channel (PUCCH: Physical Uplink Control Channel).
Control information to be transmitted on the uplink includes downlink quality information (CQI: Channel Quality Indicator), retransmission acknowledgement signals (ACK/NACK) in response to downlink shared channel (PDSCH: Physical Downlink Shared Channel)) signals and so on.
In the third-generation system (W-CDMA), it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in the LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. Also, in the UMTS network, the successor system of LTE (referred to as, for example, “LTE-Advanced” or “LTE enhancement” (hereinafter referred to as “LTE-A”)) is under study, for the purposes of further improving spectral efficiency and the peak data rate.